dttorun- Good thought. I wondered about filtration; probably a good step to try.
IRF- You raise good points. For me, the point was just economy and the fun of it. Many on the forum have had success creating their own solutions, and I thought it worth a try. Certainly, if the next cheeses turn out poorly, I'll have the cheap option to just buy some new CaCl2. I think it will work just fine, but I'm willing to risk the alternative outcome as well. Your point about minimizing the variables to worry about definitely hits home- I hadn't really thought about CaCl2 that way, but I am optimizing my rennet situation now for exactly this reason.